Conductive materials are used in a multitude of electronic devices for a variety of purposes. Many applications benefit from relatively thin conductive materials, due to one or more of shape, size or properties relative to such materials.
One type of thin conductive material that has seen extensive use involves materials having a base layer, such as a polymer or glass-type layer, with a conductive surface material. For instance, printable solution processing has been exploited to deposit various nanomaterials such as fullerenes, carbon nanotubes (CNTs), nanocrystals and nanowires for large-scale applications including thin-film transistors, solar cells and energy storage devices due to the low cost of these processes while attaining properties of those nanomaterials. In these processes, flat substrates such as glass, metals, Si wafer, and plastics have been used to hold nanostructure films Nanostructured materials are often capped with surfactant molecules to disperse the materials as separated particles in a solvent to form an “ink.” The ink is deposited onto flat substrates and followed by surfactant removal and solvent evaporation processes.
To produce high-quality films, significant efforts have been spent on ink formulation and rheology adjustment. In glass and plastics, the ink surface tension needs to match with substrates, and viscosity must be high enough to avoid surface tension-driven defects such as ring and dewetting in coating and drying processes. Therefore, various additives are incorporated in ink to tune the rheology properties. These insulating additives decrease the final film conductivity. Moreover, since surfactants are normally insulating and thus limit the charge transfer between nanomaterials, their removal can be particularly critical to resulting device performance. However, removing surfactants can involve extensive washing and chemical displacement, which often causes mechanical detachment of the film from the flat substrate. While polymer binders or adhesives can be used to improve the binding of nanomaterials to substrates, they tend to decrease the film conductivity further.
These additional procedures increase the complexity of solution processing, and result in high cost and low throughput. These and other considerations remain challenging to the design, formation and implementation of conductive materials.